Endothelial SK3 channel-associated Ca2+ microdomains modulate blood pressure.

Activation of vascular endothelial small-(KCa2.3, SK3) or intermediate-(KCa3.1, IK1) conductance Ca2+-activated potassium channels induces vasorelaxation via an endothelium-derived hyperpolarization (EDH) pathway. Although the activation of SK3 and IK1 channels converges on EDH, their subcellular effects on signal transduction are different and not completely clear. In this study, a novel endothelium-specific SK3 knockout (SK3-/-) mouse model was utilized to specifically examine the contribution of SK3 channels to mesenteric artery vasorelaxation, endothelial Ca2+ dynamics, and blood pressure. The absence of SK3 expression was confirmed using real-time quantitative PCR and Western blot analysis. Functional studies showed impaired EDH-mediated vasorelaxation in SK3-/- small mesenteric arteries. Immunostaining results from SK3-/- vessels confirmed the absence of SK3 and further showed altered distribution of transient receptor potential channels, type 4 (TRPV4). Electrophysiological recordings showed a lack of SK3 channel activity, while TRPV4-IK1 channel coupling remained intact in SK3-/- endothelial cells. Moreover, Ca2+ imaging studies in SK3-/- endothelium showed increased Ca2+ transients with reduced amplitude and duration under basal conditions. Importantly, SK3-/- endothelium lacked a distinct type of Ca2+ dynamic that is sensitive to TRPV4 activation. Blood pressure measurements showed that the SK3-/- mice were hypertensive, and the blood pressure increase was further enhanced during the 12-h dark cycle when animals are most active. Taken together, our results reveal a previously unappreciated SK3 signaling microdomain that modulates endothelial Ca2+ dynamics, vascular tone, and blood pressure. [ABSTRACT FROM AUTHOR]